The present invention relates in general to the field of DC motor control circuits. More particularly the present invention relates to an improved "H" switch circuit utilizing MOS SCR's and power MOSFETS for providing bidirectional control of DC motors, wherein a low voltage drive or control signal may be used to connect a relatively high voltage to the DC motor.
Previously there has been described an "H" switch circuit for use in reversing the motor supply voltage for bidirectional control of a DC motor. Opposing top and bottom switches coupling the DC motor input leads to a voltage source and circuit ground control the motor direction by switching voltage polarity, which in turn switches the motor's shaft rotation either clockwise or counter-clockwise. Heretofore these "H" switch circuits utilized either bipolar devices, Darlington transistors, or more recently power MOSFETS for the actual switching devices. For example, U.S. Pat. No. 4,454,454 issued to Richard J. Valentine describes an "H" switch circuit utilizing power MOSFETS for the individual switches. A recent improvement provides for the use of a MOS SCR in place of the power MOSFET for the high side switch in such a circuit. While this improved "H" circuit provides certain advantages there is an inherent limitation to the amplitude of the supply voltage which may be used in conjunction therewith due to the gate-to-cathode breakdown voltage of the MOS SCR.